1. Field of the Invention
The present invention relates to a sound receiver and directivity thereof.
2. Description of the Related Art
Conventionally, a microphone device having directivity toward a specific speaker direction has been proposed (for example, refer to Japanese Patent Laid-Open Publication No. H9-238394) as a sound input device. This microphone device is a directional microphone in which multiple microphones are arranged on a plane, and outputs of respective microphones are added through a delay circuit, respectively, to obtain an output. A silence detection function acquires a ratio between a cross-correlation function of a predetermined range of time difference between output signals of the respective microphones and a cross-correlation function of a time difference between signals corresponding to set sound source positions, and makes voice and silence determination by detecting that there is a sound source at the set position when this ratio satisfies a predetermined threshold.
However, when the microphone device described above is set in a relatively small space such as a room, the microphone device is often set on a wall of the room or on a table. It is common knowledge that if the microphone device is thus set on a wall or a table, sound clarity is negatively affected by waves reflected from the wall or the table, and when the sound is recognized by a sound recognition system, there has been a problem of deterioration in recognition rate.
Moreover, although a boundary microphone device is engineered so as to receive only a sound wave directly from a speaker without receiving waves reflected from the wall or the like, when multiple boundary microphones are used to act as a microphone array device, there has been a problem in that the directivity is not sufficiently exerted due to individual variations originated in the complicated structure of the boundary microphone. Furthermore, when the microphone array device is mounted on a vehicle, since the space of the vehicle interior is small, the effect of the reflected waves is significant, and there has been a problem in that the directivity is not sufficiently exerted.